The Green Gate Glitch is a glitch lets you open left-facing gates from the right side using precise movement and shooting a super missile at the right time.

To perform the Green Gate Glitch, stand at least a pixel behind the gate, aiming up+left, and jump. Immediately after jumping, press left, then immediately fire a Super Missile. With proper timing, the gate should open.

Note that this is also possible to do with Blue Gates as well, and if doing it with a Blue Gate it is possible to use regular missiles as well.